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Tips and questions relating to the GPS modules from SFE
By tayhoenes
I am having trouble senting commands to my EM-408 module. I am using a PIC microcontroler and it seems to be outputing the programming command words just fine...but the GPS does not seem to react to any of the commands.

I noticed that someone put a \r\n at the end of their command word. Is that needed?

By texram
Hi, tayhoenes:

Did you get your EM-408 work?
I just brought EM-408 from Sparkfun, and sent the command:
"$PSRF103,04,00,01,01*20\r\n" to turn on RMC message.
But the RMC message that I received has just date and time, and data not Valid info.
I turned off all other messages.
Did you any idea what could be wrong?

By scalegps

Yes you need to put the "\r\n" at the end of the command string. Without this carriage return\line feed pair at the end of the string the command will not be accepted.

If your RMC message just has date and time with a NV flag this normally means that you are tracking only 1 or 2 satellites. Depending on the firmware in the receiver, 1 or 2 satellites are all that is needed for date and time, while you need at least 3 SV's to get a 2D fix.

Try turning on the GSV message and see what the SV data looks like.
By texram
Hi, Scalegps:

Thanks for the reply.
Now I got the RMC message. But I couldn't figure out how to enable GGA message. I sent this command, $PSRF103,00,00,01,01*23\r\n, to GPS,
but still didn't receice GGA data. Do you have any idea?
By scalegps

Your string looks fine other than I calculate "25" as the checksum instead of "23". You might try that.

By texram
Thanks a lot, Randy, I'll try to use '25' as checksum.
By texram
HI, Randy:

I got GGA data, thanks for the suggestion.
But the MSL Altitude reading keeps changes, from about 130 to 160 (meters), the numbers of satellites used also changes (from 9 to 4). Longitude and Latitude readings are very stable. Any idea?

I only enable GGA and RMC data for receiving.